1. Field of the Invention
The present invention relates generally to the art of sputtered films and more particularly to the art of durable metal oxide films produced by magnetron sputtering.
2. Discussion of the Present Technology
Sputtered metal oxide films are well known in the art. Tin oxide, zinc oxide, titanium oxide and many other metal oxides are known to be deposited by sputtering the respective metals in an oxidizing atmosphere such as air or a mixture of oxygen and inert gas such as argon. It is also known that a metal film can be deposited by sputtering a metal in an inert atmosphere such as argon, and the metal film subsequently oxidized thermally by heating in an oxidizing atmosphere such as air.
Various metals can be deposited either as metallic films or metal oxide films depending on whether the metal cathode target is sputtered in an inert atmosphere or an oxidizing atmosphere. Generally, sputtering in an inert atmosphere, i.e. in the metallic mode, is faster and more efficient. The resulting coating is a metal film having metallic properties, i.e. generally low transmittance, high reflectance and electrically conductive. Such films are generally not very hard or durable, and are easily damaged in handling. Dielectric metal oxide films are typically high transmittance, lower reflectance and electrically insulating. However, because they are insulating, they do not deposit as efficiently by sputtering. To produce very thick metal oxide films by sputtering is inefficient, costly and may not result in a durable film. To produce very thick metal oxide films by thermally oxidizing metal films efficiently sputtered in an inert atmosphere is inherently rate-limited because oxygen may not readily penetrate beyond the initially formed surface layer of metal oxide.
The present invention involves a method of sputtering a metal target in an atmosphere sufficiently inert that sputtering is performed in the metallic mode and the film deposited is in an essentially metallic state. However, sufficient reactive gas is added to the atmosphere so that the metal film is amorphous rather than crystalline. The amorphous sputtered metal film is harder and more durable than a metal film sputtered in an atmosphere consisting of only inert gas. The amorphous sputtered metal film may be thermally oxidized more efficiently than a metal film deposited in an atmosphere consisting of only inert gas, resulting in a crystalline metal oxide film which is substantially more chemically durable than an amorphous metal oxide film deposited by sputtering metal in an oxidizing atmosphere.